Showing posts with label mindstorms. Show all posts
Showing posts with label mindstorms. Show all posts
Monday, August 30, 2010
Tutorial on Building a Thermostatic Sensor for your NXT
In this video, I take you step-by-step through the process of creating a thermostatic sensor for your NXT. Enjoy!
Sunday, January 4, 2009
The Communication Protocol
In communicating with the NXT robot, we want to keep our communication protocol as simple as possible. Through simplicity, the PC can direct more of its attention to the problem of Monte Carlo Localization (MCL), and less of its time on Bluetooth connection. The PC sends its command in the form of three integers. The first integer is the command itself, an integer from 0 to 4. The two integers that follow the command are optional parameters.
The robot’s reply is always eight integers. We need eight integers to accommodate the eight echoes that we obtain from the ultrasonic sensor.
There are five cases to consider:
The responsibility for sending the command to the robot and receiving a reply from it is shared between the Event Handler and BTCommPC classes. Upon detecting that an action event has been fired on the GUI, it is the Event Handler’s responsibility to gather the necessary information, compose the three-integer command and pass a reference to the integer array to the BTCommPC class. BTCommPC is responsible for sending the command one integer at a time to the robot and await a reply. Once a reply starts being sent, BTCommPC reads each integer, one at a time, placing them in an eight-integer array. BTCommPC then passes a reference to the array to the Event Handler.
Once the Event Handler receives a reference to the reply array, it is handler’s responsibility to disseminate it. Usually, this involves passing values back to the GUI panels and passing the ultrasonic sensor readings to the MCL class so that the MCL class can update its statistics. This command/reply process continues until the user requests that the Bluetooth connection be terminated either explicitly by pressing the disconnect button, or implicitly by terminating the program.
The robot’s program is complementary to BTCommPC’s algorithm. At first, the robot waits for a Bluetooth connection. Once a connection is made, it waits to receive its three-integer command. Once the command is received, the robot moves or turns, if necessary, and then sends back its eight-integer reply one integer at a time. The robot then waits for its next command. If the robot is commanded to terminate its Bluetooth connection, the robot sends back its acknowledgement, disconnects, and its program terminates on the brick.
More implementation to come.
The robot’s reply is always eight integers. We need eight integers to accommodate the eight echoes that we obtain from the ultrasonic sensor.
There are five cases to consider:
Description: The user requests the battery voltage
Command 0, 0, 0
Reply millivoltage, 0, 0, 0, 0, 0, 0, 0
Description: The user asks for the ultrasonic sensor to ping and report back
Command 1,0,0
Reply A series of 8 integers being the echo values
Description: The user requests that the robot move forward/backward
Command 2,distance,speed
Reply A series of 8 integers being the echo values
Description The user requests that the robot turn left/right
Command 3,angle,speed
Reply A series of 8 integers being the echo values
Description The user requests that the Bluetooth connection be terminated
Command 4,0,0
Reply 255,255,255,255,255,255,255,255
The responsibility for sending the command to the robot and receiving a reply from it is shared between the Event Handler and BTCommPC classes. Upon detecting that an action event has been fired on the GUI, it is the Event Handler’s responsibility to gather the necessary information, compose the three-integer command and pass a reference to the integer array to the BTCommPC class. BTCommPC is responsible for sending the command one integer at a time to the robot and await a reply. Once a reply starts being sent, BTCommPC reads each integer, one at a time, placing them in an eight-integer array. BTCommPC then passes a reference to the array to the Event Handler.
Once the Event Handler receives a reference to the reply array, it is handler’s responsibility to disseminate it. Usually, this involves passing values back to the GUI panels and passing the ultrasonic sensor readings to the MCL class so that the MCL class can update its statistics. This command/reply process continues until the user requests that the Bluetooth connection be terminated either explicitly by pressing the disconnect button, or implicitly by terminating the program.
The robot’s program is complementary to BTCommPC’s algorithm. At first, the robot waits for a Bluetooth connection. Once a connection is made, it waits to receive its three-integer command. Once the command is received, the robot moves or turns, if necessary, and then sends back its eight-integer reply one integer at a time. The robot then waits for its next command. If the robot is commanded to terminate its Bluetooth connection, the robot sends back its acknowledgement, disconnects, and its program terminates on the brick.
More implementation to come.
Connection, Command, and File Dump Panels
This blog entry is the continuation of my discussion of my project to demonstrate the idea behind Monte Carlo Localization (MCL) for robots using the NXT Mindstorms robot. The PC will run the MCL algorithm with the robot acting essentially like a mobile sensor platform. The PC and robot will communicate with each other over a Bluetooth connection. Here, I am going to discuss the connection panel, the command panel, and the file dump panel.
We want the Connection Panel to look like this
The single button at the top will act as both the connect and the disconnect button. The text on the button will alternate between the words connect, printed in green, and disconnect, printed in red. The status field, which cannot be edited by the user, will read either disconnected when the PC is not connected to the NXT robot, or connected when a Bluetooth connection has been established between the PC and the robot.
The only method that might need some explanation is this one:
This method is needed in case the user attempts to terminate the program before the robot is disconnected from the PC. If this should happen, we need a way to programmatically click the disconnect button before the program terminates. The doClick() method of the connectButton component does just exactly that.
I have primed the Bluetooth address field with my own NXT's Bluetooth address for the sake of personal convenience. You can change this by either commenting out or amending the following line of code.
You can download ConnectPanel.java here.
Another panel that we need is the Command panel. We want it to look like this
It has three buttons: initialize, move, and turn. The initialize button is used to re-start the MCL algorithm from scratch. The move button is used the move the robot a specified number of millimeters forward, if the distance is positive; backwards if the distance is negative. The turn button is used to turn the robot in place a specified number of degrees to the right, if the angle is negative; to the left if the angle is positive. The speed slider is used to adjust the robot’s speed.
We should emphasize that we are not trying to develop a remote control robot. Rather, the robot moves or turns in distinct stages. After each move or turn, students can observe how that move or turn has impacted the MCL algorithm. I am hoping that in this way students can learn how the MCL algorithm works through experimentation and feedback.
The following method may need some additional explanation:
A similar method also appears in the Statistics panel. This method is used to enable or disable the input components. The components are disabled whenever there is no connection between the PC and the robot; enabled whenever there is a connection between the PC and the robot. You can download CommandPanel.java here.
Another panel that we need is called the File Dump panel. We want the panel to look like this:
When the user clicks on the File Dump button, all of the statistics currently held by the MCL algorithm are written to a comma-separated value (csv) file using the index number on the spinner as part of the file’s file name. The spinner is automatically incremented to the next integer to avoid an accidental file overwrite. If the auto dump box is checked by the user, then the statistics are written to a csv file automatically after every move or turn of the robot. The spinner is automatically incremented to prevent an accidental file overwrite.
The purpose of the file dump panel is to allow the user to study the MCL algorithm's statistical data in another application such as Matlab or Excel to name two examples.
The File Dump button is always enabled, because there is always statistics to be written out to a file, even when the program is first initialized. You can download FileDump.java here.
The last panel that we will need is the Display Panel. I want to defer discussion of that panel until the next time I blog, because that panel touches very closely upon the MCL algorithm. While the class itself is not complicated as far as Java code goes, some of the things that the panel is doing might be unclear and require some explanation. If you should have any questions, please contact me at adcaine@gmail.com. See you next time.
We want the Connection Panel to look like this
The single button at the top will act as both the connect and the disconnect button. The text on the button will alternate between the words connect, printed in green, and disconnect, printed in red. The status field, which cannot be edited by the user, will read either disconnected when the PC is not connected to the NXT robot, or connected when a Bluetooth connection has been established between the PC and the robot.
The only method that might need some explanation is this one:
public void clickConnectButton(){
if(connectButton.getText().equals("Disconnect")){
connectButton.doClick();
}
}
This method is needed in case the user attempts to terminate the program before the robot is disconnected from the PC. If this should happen, we need a way to programmatically click the disconnect button before the program terminates. The doClick() method of the connectButton component does just exactly that.
I have primed the Bluetooth address field with my own NXT's Bluetooth address for the sake of personal convenience. You can change this by either commenting out or amending the following line of code.
addressField.setText("00:16:53:00:57:37");
You can download ConnectPanel.java here.
Another panel that we need is the Command panel. We want it to look like this
It has three buttons: initialize, move, and turn. The initialize button is used to re-start the MCL algorithm from scratch. The move button is used the move the robot a specified number of millimeters forward, if the distance is positive; backwards if the distance is negative. The turn button is used to turn the robot in place a specified number of degrees to the right, if the angle is negative; to the left if the angle is positive. The speed slider is used to adjust the robot’s speed.
We should emphasize that we are not trying to develop a remote control robot. Rather, the robot moves or turns in distinct stages. After each move or turn, students can observe how that move or turn has impacted the MCL algorithm. I am hoping that in this way students can learn how the MCL algorithm works through experimentation and feedback.
The following method may need some additional explanation:
public void setButtonsEnabled(boolean setting){
initialize.setEnabled(setting);
move.setEnabled(setting);
turn.setEnabled(setting);
speedSlider.setEnabled(setting);
}
A similar method also appears in the Statistics panel. This method is used to enable or disable the input components. The components are disabled whenever there is no connection between the PC and the robot; enabled whenever there is a connection between the PC and the robot. You can download CommandPanel.java here.
Another panel that we need is called the File Dump panel. We want the panel to look like this:
When the user clicks on the File Dump button, all of the statistics currently held by the MCL algorithm are written to a comma-separated value (csv) file using the index number on the spinner as part of the file’s file name. The spinner is automatically incremented to the next integer to avoid an accidental file overwrite. If the auto dump box is checked by the user, then the statistics are written to a csv file automatically after every move or turn of the robot. The spinner is automatically incremented to prevent an accidental file overwrite.
The purpose of the file dump panel is to allow the user to study the MCL algorithm's statistical data in another application such as Matlab or Excel to name two examples.
The File Dump button is always enabled, because there is always statistics to be written out to a file, even when the program is first initialized. You can download FileDump.java here.
The last panel that we will need is the Display Panel. I want to defer discussion of that panel until the next time I blog, because that panel touches very closely upon the MCL algorithm. While the class itself is not complicated as far as Java code goes, some of the things that the panel is doing might be unclear and require some explanation. If you should have any questions, please contact me at adcaine@gmail.com. See you next time.
Wednesday, December 31, 2008
Important Links
Here are some very useful links to get information about programming the NXT in the Java Language:
- SourceForge From here, you can download the jar files as well as the brick's firmware to get you started programming in Lejos -- Java for the Mindstorms NXT brick
- Setup Tutorial From this website, you can learn how to properly set up your brick with the firmware, and correctly get Eclipse (a Java development environment) working properly
- Forum In this forum, you can communicate with other developers who use Lejos to program the NXT brick
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